While working on another tutorial, Sudar Muthu came across a simple way of using the Yahoo Query Language to "query, filter, and join data across Web services". The Arduino can then parse the JSON reponse and return the results. When replicating this yourself, take heed of Sudar's notes about memory space and perhaps the idea of adding an LCD shield for results output.
For more information, including links to Sudar's code and the YQL system, click here. And for more, we're on twitter and Google+, so follow us for news and product updates as well.
When Ethernet-enabled projects outgrow the memory space available from normal Arduino-compatible boards, running out of program and flash memory space - it's time to upgrade to the Freetronics EtherMega:
Quite simple the EtherMega is the fully-loaded Arduino-compatible board on the market today. Apart from being completely Arduino Mega2560-compatible, it includes full Ethernet interface, a microSD card socket, full USB interface, optional Power-over-Ethernet support and still has a circuit prototyping area with extra I2C interface pins. So if your project is breaking the limits, upgrade to the EtherMega today.